Intro
The water hardness in my home (Gobi) is around ~600 ppm. In Chennai where I live, it’s around 800 ppm (metro water). Half the people get purified water for their drinking; there is business for those who supply water, while the other half get a water-purification system installed in their homes by a vendor/company that produces it. We can build a DIY homemade purifier. It’s a new challenge, a chance to learn new things, and cheaper than buying ready-made.
Water “hardness” is simply the concentration of dissolved calcium and magnesium ions in water. It is usually expressed in mg/L or ppm as CaCO₃.
• Soft: 0–60 ppm
• Moderately hard: 61–120 ppm
• Hard: 121–180 ppm
• Very hard: > 180 ppm
Hard water leaves scale in pipes and appliances and can affect taste, so reducing hardness is one of the main goals of an RO unit.
Components needed
Coming to things that are needed for the DIY setup, I need to buy the following items.
| S.No | Item | Qty | Rate (₹) | Amount (₹) | Why it’s used |
|---|---|---|---|---|---|
| 1 | Wall-mount plate (12″) | 1 pc | 140.00 | 140.00 | Base plate to fix the RO unit on the wall |
| 2 | BlueShell booster pump | 1 pc | 850.00 | 850.00 | Raises pressure so the RO membrane works efficiently |
| 3 | BlueShell 100 GPD RO membrane | 1 pc | 850.00 | 850.00 | Main purification element that removes dissolved salts |
| 4 | GAC inline cartridge | 1 pc | 90.00 | 90.00 | Granular activated-carbon pre-filter for chlorine removal |
| 5 | CTO 10″ carbon block | 1 pc | 90.00 | 90.00 | Carbon block for chlorine, taste, odour removal |
| 6 | Membrane housing (1812) | 1 pc | 130.00 | 130.00 | Holds and seals the RO membrane |
| 7 | Accord 1.5 A SMPS | 1 pc | 300.00 | 300.00 | 24 V DC power supply for pump & UV lamp |
| 8 | UV-chamber set (11 W) | 1 set | 300.00 | 300.00 | UV-C sterilization of product water after RO |
| 9 | Handheld TDS meter | 1 pc | 450.00 | 450.00 | Tests input/output water quality (ppm) |
| 10 | Tubing cutter | 1 pc | 30.00 | 30.00 | Gives clean, square cuts on RO tubing |
| 11 | Alkaline remineralizer (4″) | 1 pc | 250.00 | 250.00 | Adds minerals and raises pH after RO |
| 12 | 10″ filter housings | 3 pcs | 120.00 | 360.00 | Hold sediment, CTO and GAC cartridges |
| 13 | ¼″ RO tubing (≈ 5 m) | 2 coils | 40.00 | 80.00 | Connects all filters, pump, membrane and faucet |
| 14 | Two-side connectors | 2 pcs | 5.00 | 10.00 | Straight unions to join tubing sections |
| 15 | Pump elbows | 2 pcs | 10.00 | 20.00 | 90° elbows for pump inlet/outlet to tubing |
| 16 | Membrane elbows | 2 pcs | 5.00 | 10.00 | Elbows that screw into membrane housing ports |
| 17 | Housing elbows | 5 pcs | 9.00 | 45.00 | Elbow fittings for pre-filter housings |
| 18 | Inlet-valve set | 1 set | 120.00 | 120.00 | Shuts off/isolates the water supply to the RO unit |
| 19 | Post-carbon cartridge | 1 pc | 80.00 | 80.00 | “Polishing” filter that improves taste after RO |
| 20 | C-clamp | 2 pcs | 10.00 | 20.00 | Hardware for mounting the wall plate/housing |
| 21 | X-clamp | 2 pcs | 10.00 | 20.00 | Additional mounting support for the RO assembly |
| 22 | PTFE (Teflon) tape | 10 rolls | 10.00 | 100.00 | Seals threaded joints to prevent leaks |
| 23 | General-purpose tape | 1 roll | 10.00 | 10.00 | Miscellaneous binding/labelling |
Total value of cash-memo items: ₹4,360
Bill of the items bought.
How all the parts are plumbed – step-by-step
We have 3 big housings. We put the following filters inside them and connect them sequentially. Using similar housing to the spun filter, we fit the other filters and connect them up until the motor.
Sediment (Spun) filter
The very first stage. It traps visible particles such as sand, rust and silt so that none of the downstream cartridges get clogged prematurely.CTO 10″ carbon-block filter
Removes chlorine, taste and odour. Chlorine must be taken out here because it can irreversibly damage an RO membrane.GAC (pre-carbon) filter
A second carbon stage that “polishes” the water and adsorbs any remaining organic chemicals that slipped past the CTO block.Booster pump (motor) + low-pressure cut-off
Right after the pre-carbon filter the water enters the BlueShell booster pump.
• The pump raises the feed-water pressure to ~80 psi so that the RO membrane can work efficiently.
• Placing it here ensures that only pre-filtered, de-chlorinated water passes through the pump head, protecting the pump and its check-valves from grit or chlorine attack.RO membrane housing with 100 GPD membrane
Under high pressure the semi-permeable membrane now removes dissolved salts, heavy metals, fluoride, nitrates, etc.
This (following image) is how we fit the RO membrane; we need to make sure the waste-water port is not the one we use.
Another thing to note: The waste (concentrate) port coming out of the housing is fitted with a flow-restrictor to maintain the required pressure differential.
Post-carbon (polishing) filter
The first stage on the product-water side. It adsorbs any residual gases and improves the taste and smell of the permeate coming out of the RO membrane.Alkaline remineralizer
Adds back healthy minerals (calcium, magnesium, potassium) and gently increases the pH so the water is no longer slightly acidic.UV-C chamber (11 W)
The final barrier. Ultraviolet light disinfects the remineralized water, inactivating any bacteria, viruses or cysts that might have slipped through or grown in the storage tank.
From the UV outlet the water goes to the water storage through pipes.
I also got a pH tester, measured the colour.
The tester uses a liquid reagent: add 2 drops to 5 ml of water and compare the resulting colour to the chart in the pH tester.
• Raw inlet water: pH ≈ 7.4 (greenish)
• RO permeate before remineralizer: pH ≈ 6.3 (yellow)
• Final water after remineralizer: pH ≈ 7.2 (light green)
This shows the remineralizer is doing its job—bringing the pH back close to neutral so the water is neither acidic nor alkaline.
Final setup
Mounting
Mounted everything with a zip-tie to a window in the kitchen. When everything is connected, leave it running for 20 mins; you can immediately detect the change. The TDS of the purified drinking-water bottle that we buy is about 25 ppm, I get 19 ppm with this setup.
References
Central Pollution Control Board India
https://cpcb.nic.in/wqm/BIS_Drinking_Water_Specification.pdf
Personal Update
Feel like everything is stagnant… even though there’s small progress. If you are working for big corpora, you are just a row in an Excel sheet. The feeling resonates more and more reading trending Hacker News and things that happen around in personal experience. As for me, as always trying to make time for open source and my hobbies… in the increasing midst of responsibilities coming towards me. I also almost got into a marriage arranged by my dad, forced to go see them… the girl & girl’s family like me and are trying to convince me into marriage, my dad doing all his best to set this up, fighting with me, etc. The girl is good too, perfect for family, they are a distant relative, born in 2000… But there are other plans/God has other plans. ~future me reading this… what happened?
Talked to an old friend; he said he discovered a private office Wi-Fi password written on a note and has been using it secretly. That reminded me of the first time I cracked a WPA endpoint in 2015. It felt great back then. We had BSNL broadband—“unlimited” but stuck at 60 kbps. I used to combine my connection with my neighbor’s Wi-Fi for maximum speeds. Those were fun times; I even made a mod of an application that combined network connections…Long story short, he reminded me of Wi-Fi hacking. When I got back home to Gobi, I brought out my old Wi-Fi packet-injecting dongle and Linux laptop to chennai. I found a couple of neighbors’ Wi-Fi networks. After shutting down my unreliable Airtel connection in Chennai, I switched to unlimited mobile data (from previous posts), so I decided to use their Wi-Fi (nobody uses wpa3.. even the new routers comes with wpa2, you can easily capture the handshake and crack it.. I used hashcat, its super fast and reliable). While on their network, I logged in to their router, checked their device list, and configured Wi-Fi settings for a longer range on 2.4 GHz by switching between 20 Hz and 40 Hz channels.. Some of the closest Wi-Fi access points are 5 GHz and offers low latency too.. By seeing the device list, I was able to mimic their device name and avoid being caught. For example: “smart-camera.”.. to be fair, I would just use them for internet..nothing more..nothing less.